Hari also apologised for editing the Wikipedia entries of people he had clashed with, using the pseudonym David Rose, "in ways that were juvenile or malicious", saying he was "mortified to have done this". He admitted calling "one of them antisemitic and homophobic, and the other a drunk".

Hari is also handing back the George Orwell prize he won as "an act of contrition for the errors I made elsewhere, in my interviews" and will undertake "a programme of journalism training" during his leave of absence.

It is understood that provided no more damaging revelations emerge about the journalist during his unpaid leave, the Independent editor, Chris Blackhurst, will allow him to return to the paper.

In a statement, the paper said that Hari "admits the central accusations made against him, that of embellishment of quotations/plagiarism, and that it was he who used the pseudonym David Rose to attack his critics".

In a formal apology published on the Independent's website, Hari admitted he did "two wrong and stupid things" – the first, inserting quotes that were not his own into interviews, and the second, deliberately editing the entry on himself in Wikipedia and using an alter ego to edit other people's entries.

"I took out nasty passages about people I admire – like Polly Toynbee, George Monbiot, Deborah Orr and Yasmin Alibhai-Brown … but in a few instances, I edited the entries of people I had clashed with in ways that were juvenile or malicious: I called one of them antisemitic and homophobic, and the other a drunk." He added: "I am mortified to have done this, because it breaches the most basic ethical rule: don't do to others what you don't want them to do to you. I apologise to the latter group unreservedly and totally."

Hari was suspended from the Independent in the summer following accusations on Twitter and blogs that some of his interviews were not entirely his own work.

Hari responded in an Independent blogpost that the accusations were "totally false" and said he had never taken words from "another context and twisted them to mean something different". But he admitted he had substituted quotes he had got from his own interviews with similar quotes from the author's own work, or from other interviews if they were more clearly expressing the same point. In his apology, he said he admitted that was wrong to say the practice of substituting quotes gained through a face-to-face interview with other quotes was justified because it gave "the clearest possible representation of what the interviewee thought".

"An interview isn't an x-ray of a person's finest thoughts. It's a report of an encounter. If you want to add material from elsewhere, there are conventions that let you do that," Hari said. "You write 'she has said,' instead of 'she says'. You write 'as she told the New York Times' or 'as she says in her book', instead of just replacing the garbled chunk she said with the clear chunk she wrote or said elsewhere."

In one interview, with journalist Ann Leslie, critics claimed more than 500 words of Hari's near-5,000 word piece came from an article she wrote in the Daily Mail.

When the allegations first surfaced the then editor of the paper, Simon Kelner, described the plagiarism row as "fabricated anger" and "politically motivated".

His successor Blackhurst took a different view, suspending the journalist and ordering an internal inquiry headed by Whittam Smith.

Hari said "the worst part" was thinking about "readers" who admired his articles and believed in the causes he championed. "I hate to think of those people feeling let down, because those causes urgently need people to stand up for them," Hari wrote.

He said he also felt bad for his colleagues at the paper. "I am horrified to think that what I have done has detracted from the way they get it right every day," he wrote. "I am sorry."

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